With a growing demand for improvement of connectivity or convenience of operation in an optical transmission system that uses optical fibers in recent years, attention has been given to an optical transmission system that provides functionality of Optical Add-Drop Multiplexer (hereinafter called OADM) wavelength or wavelength band and variable wavelength functionality for optical signals on a same fiber transmission path. In particular, with improvement of resolution by introduction of a Wavelength Selective Switch (hereinafter called WSS) technology, further convenience or connectivity of an optical transmission system that employs an optical add-drop multiplexer (hereinafter referred to as OADM branching device) has become improved.
On the other hand, introduction of a wavelength multiplexing technology and OADM functionality has made a system configuration, such as wavelength band connection management, complex with increase in the number of stations, and it has become essential to provide a function of monitoring an operation state of an optical transmission system in order to deal with a failure or reconfiguration.
PTL 1 describes an optical signal level adjustment system including a signal interruption detection unit that detects a signal interruption on a wavelength-block basis in a terminal station device, and transmitting a control signal that adjusts intensity of dummy light of a terminal station device from which a signal interruption is detected.